South Korea and the US have signalled their support for a land-based radio navigation system as incidents of GPS disruption become more frequent

South Korea is planning to invest in a land-based radio navigation system whose underlying technology dates back to the Second World War, amidst growing concern over the vulnerability of the satellite-based Global Positioning System (GPS) to jamming and other interference.

The move follows renewed US interest in the system, called eLoran, an updated version of the Loran technology developed by the US in the 1940s.

Second World War-era tech

Loran (LOng RAnge Navigation) was itself modelled on the Gee system used by the Royal Air Force starting in 1942, with the last Gee transmitter going off-air in 1970.

Like GPS, Loran determines position by measuring the timing difference between signals whose point of origin is known, but it relies on powerful land-based transmitters rather than the much weaker signals emitted by GPS satellites.

GPS relies on satellite signals that can easily be blocked.

The system was widely used for both military and commercial sea navigation up until the 1990s, when the spread of cheap satellite-based systems caused a rapid drop-off.

Some transmitters for Loran-C, the most recent version of the system introduced in 1957, are still in operation, but most have been decommissioned due to their cost. The US and Canada ceased operations in 2010 and most European countries shut down their stations at the end of 2015.

The UK still maintains a transmitter near Anthorn, in Cumbria, but on its own it can only be used for timing purposes and not for navigation.

GPS disruption

With most sea traffic now relying on GPS, governments have found it difficult to justify continuing to fund Loran. But the weak signals used by GPS and the European Galileo system can easily be disrupted by inexpensive equipment, and incidents of disruption are becoming increasingly frequent.

South Korea last year reported that hundreds of fishing vessels were forced to return to port early after their GPS signals were jammed by North Korean hackers. North Korea denied responsibility.

In June this year the US Coast Guard said more than 20 ships in the Black Sea experienced disruption. The agency said an unnamed port experienced GPS disruption for several hours in 2014 with another facing a similar issue in 2015.

South Korea’s Ministry of Oceans and Fisheries now says it plans to set up three sites for eLoran trials by 2019 and further sites after that.

The ministry told Reuters it was contending with opposition from residents of Gangwha Island off the peninsula’s west coast to construction of the antenna there.

“The residents on the island are strongly opposed to having the 122 to 137 meter-high antenna,” said the ministry’s Lee Byeong-gon.

eLoran gets US backing

South Korea’s move follows the US House of Representatives’ decision in July to pass a bill that backs the establishment of an eLoran system.

The bill was a direct response to the concerns of US security and intelligence agencies over growing threats to GPS disruption.

So far none of those initiatives has succeeded in gaining the long-term backing that would be necessary to set up and operate the necessary chains of transmitters.

Commercial shipping is now largely dependent on satellite navigation systems.

A UK-US joint venture called Taviga is also investigating the private operation of an eLoran system which could include acquiring and operating some of the stations decommissioned by European governments.

Taviga was formed in December 2015 ahead of the shutdown of most of Europe’s Loran-C at the end of that month.

Cheap GPS blockers

In the meantime the threat to GPS grows ever more pressing, with short-range GPS jamming now common.

GPS jammers are available online for under £100 and are typically used by drivers with employer-installed GPS trackers on their cars who want to do a bit of moonlighting, according to Professor David Last of the UK’s GLA.

But even these short-range blockers show how vulnerable GPS is and demonstrate the need for a backup system, he said at the time of the 2013 eLoran trials.

“The guy who simply wants to jam his own tracking system has no control over what parts of the critical national infrastructure that jammer takes out,” Last said.

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